This invention relates to an improved process for preparing rubber-modified polymeric compositions as well as the compositions prepared thereby. Specifically, it relates to polymers modified with grafted rubbery polymers, said grafted rubbery polymers being formed from hydroperoxidized rubbery polymer intermediates.
Rubber-modified polymer compositions are well-known in the prior art. Exemplary of such compositions are those comprising homopolymers and interpolymers of monovinylidene aromatic monomers and a reinforcing, modifying rubbery polymer. One technique for preparing such compositions involves polymerizing the monomers employed to prepare the matrix polymer in the presence of a hydroperoxidized rubbery polymer intermediate. Such an intermediate may be prepared by one of several techniques involving singlet oxygen induced hydroperoxidation. The process results in grafted rubbery polymers in a matrix polymer and permits precise control of the degree of rubber grafting employed.
Examples of previously known processes include those disclosed by U.S. Pat. Nos. 3,115,418; 3,925,076; 3,252,880; 3,081,242; and 3,484,353, the teachings of which are incorporated herein in their entirety by reference thereto.
Previously known processes of preparing rubber-modified monovinylidene aromatic polymer compositions utilizing hydroperoxidized rubbery intermediates have produced compositions having acceptable physical properties at low hydroperoxide levels less than about 15 micromoles (mmole) hydroperoxide/gram hydroperoxidized rubber. However, at higher rubber hydroperoxide graft levels previous processes have resulted in the preparation of compositions that are deficient in certain physical properties, especially toughness as measured for example by Izod impact strength.
As an explanation of this phenomenon, it is theorized that at high graft levels, the grafted polymer chains become crowded due to a lack of available rubber surface to which bonding may occur. Consequently the rubber membrane is subjected to greater stress and may even be ruptured or at least may be more easily broken when subjected to environmental forces such as shearing forces encountered during the polymerization process. The resulting smaller sized rubber domains apparently no longer contribute significantly to toughening of the matrix polymer.
It would be desirable to provide a rubber modified polymeric composition containing high levels of grafted styrenic polymer that avoids the detriment of reduced toughening ability.
In addition, it would be desirable to provide an improved process for the solution or bulk polymerization of polymers employing hydroperoxidized rubbery intermediates to obtain impact modified polymers having improved physical properties. Such polymer products may be usefully employed as injection molding resins, extrusion molding resins and in other applications.